1. Field of the Invention
The invention relates to a method for production of pitches with modified properties, and to the use of these pitches.
2. Brief Description of the Background of the Invention Including Prior Art
The use of pitches and of pitch-like residue from the upgrading of coal and from the processing of mineral oils is extremely varied. In addition to their use in construction as binders, corrosion protection agents, setting agents and insulating agents, their use is of particular interest in connection with carbon or, respectively, carbon-mold bodies. There have been numerous attempts to modify the pitches in order to improve the desired properties, since the properties of the available pitches do not always correspond to the requirements, necessities and desires of further processing operations. The coking properties of pitches can be modified by the separating of undesired components such as, for example, ash forming materials, and of fractions that are insoluble in quinoline. Furthermore, a modification by thermal treatment and hydrogenation has been described.
Hydrogenation is the most expensive and costly method in terms of equipment and processing requirements. The influence of the alkylation of benzene insoluble (BI)/quinoline soluble (QS) (.beta.-resins) and of quinoline insoluble fraction (QI) from coal tar pitch has also been investigated (Fuel 1974, 53(4), 253-7). For example, the alkylation with alkyl halides improves the solubility in benzene. However, in contrast to the results from hydrogenation, no improvement of the graphitizing properties and of the coke structure is seen. Similar investigations with quinoline insoluble fractions of petroleum pitches have been performed (Fuel 1975, 54(4), 265-8). During the alkylation with potassium and ethyl iodide, 60% of the pitch can be transformed into a benzene soluble material. The coking properties, however, are not improved. The alkylated pitch is again de-alkylated by catalytic hydration.
Material that is soluble but has bad graphitizing properties is obtained by the akylation of asphalt with dodecylchloride with a Friedel-Crafts reaction (Nenryo Kyokai-Shi 1975, 54(12), 994-1001). The quality improvement of petroleum and coal tar pitch by alkylation of a sodium containing pitch/solvent mixture with ethyl iodide followed by catalytic hydrogenation is described in the Japanese Patent No. 7641,129. Quinoline insoluble fractions (30 weight percent quinoline insoluble (QI)) can be brought into solution by this treatment in an amount of up to 86 weight percent. The needle coke or acicular coke can be produced from the pitch free if quinoline insoluble content in a yield of 96 weight percent. The improved coking properties are to be assigned to the separation of the quinoline insoluble portion and to the hydrogenation, since the alkylation with ethyl iodide in the presence of sodium by itself does not result in an improvement in the coking behavior, as was set forth above.
In fact, the alkylation by a Friedel-Crafts reaction improves the solubility even of pitch fraction insoluble in quinoline. However, the coking behavior is not improved (Sekioyu Gakkai-Shi 1978, 21(1), 16-21). The coking properties become clearly worse. Even the starting pitch material can be coked to an anisotropic coke, but a non-graphitizable coke is obtained from the alkylated pitch.